Friday, March 19, 2010

ever-fascinating hobbits

Brumm, Adam, Gitte M. Jensen, Gert D. van den Bergh, Michael J. Morwood, Iwan Kurniawan, Fachroel Aziz, and Michael Storey
2010 Hominins on Flores, Indonesia, by one million years ago. Nature doi:10.1038.

Nature's advanced on-line publishing has an article by Brumm et al. on the Flores hominins, with news of stone artifacts from the site of Wolo Sege. The artifacts were found below a volcanic layer dated by Ar/Ar to 1.02 +/- 0.02 Mya. Human evolution is not my research focus (although I follow these debates with interest because I teach all the BioAnth classes here), but my attention was caught by the following:

Previously, the earliest stone artefacts at Mata Menge, associated
with the fossilized remains of S. [Stegodon] florensis florensis, as well as the absence of artefacts from Tangi Talo with its pygmy S. sondaari and giant tortoise, suggested hominin colonization of Flores between,0.9 and 0.88 Myr ago3–6,10 (Fig. 5). On this basis, the faunal turnover that occurred in the Soa Basin at this time was attributed to the arrival of this new predator, although it may have been hastened by a major volcanic eruption that blanketed the area9,18,19. It is now clear, however, in light of the evidence from Wolo Sege, that hominins
were present on Flores by 1 Myr ago. This suggests that the nonselective, mass death of S. sondaari and giant tortoise, associated with stratigraphic evidence for a major volcanic eruption at Tangi Talo ,0.9 Myr ago10, could represent a localized or regional extinction, and that the faunal turnover may have been a result of climate change, volcanic activity or some other natural process or event (Fig. 5). (Brumm et al. 2010:3)

The authors may be right, but just because there was a long period of co-existence between the tortoise, dwarf stegadons, and hominins, doesn't necessarily mean that early hominins had little or no role in the eventual extinction, or that climate changes was the only or primary cause of faunal turnover. Certainly, it appears from this evidence that faunal change was not the result of initial colonization of the island by hunters, but there are many examples of longer-term processes that lead to extinction. Changes in hominin population density, or technology, or hunting behavior, could all lead to hominin-caused extinctions, long after initial colonization. It's also possible that the natural disasters mentioned in the text would not have affected the faunal community so drastically, had there not been significant hominin predation.

My absolute favorite anthro blog, John Hawks' Paleoanthropology Weblog, had this to say about the finds:

I discussed this with my graduate seminar yesterday. The long persistence of this toolmaking culture, in what must have been a rather small human population, is weighing on my mind. Were there recurrent contacts from Java, keeping the population going? How dependent were these people on their tools?

Hominin predators can lead to unstable dynamics -- most predators will undergo predator-prey cycles, but humans can switch to other resources and continue to press a small prey species to extinction. The long persistence of tasty animals on Flores in the presence of hominins suggests that the subsistence practices of these hominins were different in some ways from later humans.

Again, I'm not sure I agree, although the issue of tool dependence, I believe, is a critical one. I think we know far to little about the population dynamics on Flores to conclude that their subsistence practices were different than later humans, just because the larger prey species persisted. How big were the hominin populations, relative to the stegadon populations? Would stegadons and giant tortoises actually have been the highest-ranked prey, when smaller animals may have easily fed such small populations of hominins? And, like I said before, are we actually certain that hominin predation wasn't having a strong negative impact on the prey populations?

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